.».,. 


IMAGE  EVALUATION 
TEST  TARGET  (MT-3) 


A 


%  .% 


1.0 


I.I 


11.25 


-Sis 

^    1^    12.0 


U    IIIIII.6 


III 


V 


qv 


:1>^ 


:\ 


\ 


V 


4^ 


CIHM/ICMH 

Microfiche 

Series. 


CIHM/ICIVIH 
Collection  de 
microfiches. 


Canadian  institute  for  Historical  lyAicroreproductions  Institut  Canadian  da  microraproductions  historiquas 

1980 


Technical  Notes  /  Notes  techniques 


The  Institute  has  attempted  to  obtain  the  best 
original  copy  available  for  filming.  Physical 
features  of  this  copy  which  may  alter  any  of  the 
images  in  the  reproduction  are  checked  below. 


L'Institut  a  microfilm*  le  meilleur  exemplaire 
qu'il  lui  a  At«  possible  de  se  procurer.  Certains 
dAfauts  susceptibles  de  nuire  A  la  quality  de  la 
reproduction  sont  not^s  ci-dessous. 


n 


Coloured  covers/ 
Couvertures  de  couleur 


Coloured  maps/ 

Cartes  gdographiques  en  couleur 


n 


Coloured  pages/ 
Pages  de  couleur 


Coloured  plates/ 
Planches  en  couleur 


0       Pages  discoloured,  stained  or  foxed/ 
Pages  d6color6es,  tachetAes  ou  piquAes 


D 


Show  through/ 
Transparence 


D 


Tight  binding  (may  cause  shadows  or 
distortion  along  interior  margin)/ 
Reliure  serrd  (peut  causer  de  I'ombre  ou 
de  la  distortion  le  long  de  la  marge 
int^rieure) 


D 


Pages  damaged/ 
Pages  endommagies 


D 


Additional  comments/ 
Commentaires  suppl6mentaires 


Bibliographic  Notes  /  Notes  bibliographiques 


D 
D 


Only  edition  available/ 
Seule  Edition  disponible 


Bound  with  other  material/ 
Reli6  avec  d'autres  documents 


n 


Pagination  incorrect/ 
Erreurs  de  pagination 


Pages  missing/ 
Des  pages  manquent 


D 


Cover  title  missing/ 

Le  titre  de  couverture  manque 


D 


Maps  missing/ 

Des  cartes  g^ographiques  manquent 


D 


Plates  missing/ 

Des  planches  manquent 


D 


Additional  comments/ 
Commentaires  suppiAmentaires 


The  images  appearing  here  are  the  best  quality 
possible  considering  the  condition  and  legibility 
of  the  original  copy  and  In  keeping  with  the 
filming  contract  specifications. 


Las  images  suivantes  ont  At*  reproduites  avec  le 
plus  grand  soin,  compte  tenu  de  la  condition  at 
de  la  nettett  de  I'exemplaire  film*,  et  en 
conformit6  avec  les  conditions  du  contrat  de 
filmage. 


The  last  recorded  frame  on  each  microfiche  shall 
contain  the  symbol  — ►  (meaning  CONTINUED"), 
or  the  symbol  y  (meaning  "END"),  whichever 
applies. 


Un  dee  symboles  sulvants  apparattra  sur  la  der- 
niiro  image  de  cheque  microfiche,  selon  le  cas: 
le  symbols  — ►  signlfie  "A  SUIVRE",  le  symbols 
V  signlfie  "FIN". 


The  original  copy  was  borrowed  from,  and 
filmed  with,  the  kind  consent  of  the  following 
institution: 

National  Library  of  Canada 


L'exemplaire  film*  fut  reproduit  grAce  A  la 
gAnirosit*  de  I'Atablissement  prAteur 
suivant  : 

Bibiiothique  natlonale  du  Canada 


Maps  or  plates  too  large  to  be  entirely  Included 
In  one  exposure  are  filmed  beginning  In  the 
upper  l«ft  hand  corner,  left  to  right  and  top  to 
bottom,  as  many  frames  as  required.  The 
following  diagrams  illustrate  the  method: 


Les  cartes  ou  les  planches  trop  grandes  pour  Atre 
reproduites  en  un  seul  cilch*  sont  fllmies  A 
partir  de  I'angle  supArieure  gauche,  de  gauche  A 
droite  et  de  haut  en  bas,  en  prenant  le  nombre 
d'Images  nicessaire.  Le  diagramme  suivant 
illustre  la  mithode  : 


1  2  3 


1 

2 

3 

4 

S 

6 

BULLETIN  OF  THE  GEOLOGICAL  SOCIETY  OF    AMERICA 
Vol.  6,  pp.  357-366,  pls.  15,  16 


PRE-PALEOZOIC  DECAY  OF  CRYSTALLINE  ROCKS  NORTH 

OF  LAKE  HURON 


BV 


ROBERT  BELL 

ASSISTANT   DIRECTOR   OF   THE  GEOLOGICAL  SURVEY  OP  CANADA 


ROCHESTER 
rUBLISHED  BY  THE  SOCIETY 
.     March,  1894 


aammmmfi- 


BULLETIN    OF   THE   GEOLOGICAL   SOCIETY   OF  AMERICA 

Vol.  5,   pp.  357-366,  PLS.   15,   16  MARCH  24,  1894. 


PRE-PAr.EOZOrc  DECAY  OF  CRYSTALLINE  UOCKS  XOHTH 

OF  LAKE  irURON  j 

HY    IIOHKHT   BKLL  I 

ASSI.SIA.NT    DlllKCI'OH   Ol"   THE  OKOIAMUtA  I,   SritVKY    <)l'   (  ANADA 

I 

(Ei'dd  hefoir  the  Soc.ietij  Decemhcr  iS,  JSO.l)  ,  j 

COXTKXTS      •  .  j 

Relation  of  Arclu'iin  to  I'iiloozoic  liocks ,'{.>7  ! 

I'Aidonce  of  i)r('-I'iileozi)io  Decay 1558  j 

Wlit-re  ln'Mt  <lis|)liiyi'(l ;i."),s 

"Ovens"  or  I'its  of  Decay .%">8  i 

UocUk  of  the  lluronian  15elt ;!.")()  j 

Ancient  Erosion ;!")(l 

Typical  Krosion  Surface :{.')!) 

("onditions  alfectin^r  l"-i'osion .'ifil 

Contacts  of  Arcliean  with  I'aleo/.oic  llocks ;i(i2 

River  and  Lake  (Miannels  due  to  Hock  Decay ;)((4 

Ahsence  of  I'aieo/.oic  Deposition  and  its  Sii;nilicance .'[(id 

Krt"ect  of  ylaciai  Denudation ."!(>(! 


IvKI. ATION    OK    AkcIIKAN    TO    1*AI.K()Z<)I(;    HoCKS. 

Li  all  parts  of  Canada  wbei'o  tlio  Paleozoic  strata  coiiie  in  contact  with 
the  underlying  Archoan  rocks  the  latter  appear  to  pass  i)eneath  them 
with  very  luiicli  the  same  <'ontour  or  slo[tc  as  that  of  tlieir  modern  sur- 
face. It  appears  evident  that  those  ancient  stratified  or  laminated  rocks 
have  been  tilted  to  their  present  lii«;h  angles,  and  that  their  included  in- 
trusive masses,  whether  of  granite  or  green.stone,  and  even  most  of  th(>ir 
dikes,  have  occupied  their  pnjsent  positions  relatively  to  each  other  before 
the  commencement  of  Paleozoic  time,  excepting  in  cnses  where  faulting 
has  taken  place.  Not  only  is  this  so,  l)ut  at  that  early  date  they  appear 
to  have  lieen  worn  down  l)y  denudation  to  sotnething  like  their  present 
superticiai  aspect. 

What  has  become  of  the  vast  amount  of  debris  resulting  from  thi.« 
denudation  ?    Tliis  is  a  prol)lem  t)f  .Vmericau  geology  wliich  has  not 

L-BvLL.  Gkol.  Soc.  Am.,  Vol.  5,  1893,  (357) 


358      R.BELL — PRE-PALEOZOIC    DECAY    OF   CRYSTALLINE    ROCKS. 

yet  received  much  explanation.  Between  the  time  of  the  folding  of  the 
Huronian  rooks  and  the  deposition  of  the  earhcst  fossihferous  beds  there 
must  have  been  an  interval  much  "greater  than  is  commonly  suppo.sed. 
Throughout  the  vast  region  of  Canada  occupied  by  the  Archean  rocks 
the  attitude  of  the  Huronian  and  Laurentian  strata  generally  approaches 
the  vertical,  and  their  surface  has  generally  b(;en  cut  down  to  nearly  a 
horizontal  outline,  which  is  only  slightly  raised  above  the  scalevel. 

Lower  Silurian  strata,  csi)ccially  limestone,  unaltered  and  full  of  fossils, 
may  be  seen  in  many  places,  resting  almost  horizontally  upon  the  up- 
turned and  denuded  edges  of  the  crystalline  rocks,  and  yet  the  former 
contain  but  few  fragments  of  the  older  terrancs,  and  they  occur  only  at 
the  very  contact,  showing  that  the  latter  had  a  hartl  and  naked  surface 
when  the  Paleozoic  rocks  were  l)eing  deposited  upon  them. 

Evidence  of  pre-Paleozoic  Decay. 

MHiere  bed  displayed. — The  evidence  of  pre-Palcozoic  decay  of  the  an- 
cient surface  is  more  discernible  upon  the  surfaces  of  ma.sses  of  intrusive 
granite  than  upon  gneiss  or  other  foliated  rocks.  The  reason  of  this 
seems  to  be  that  in  the  bottom  of  the  deep  sea,  where  the  eating  away  of 
the  rocks  appears  to  have  taken  place,  the  granite  was  more  susceptible 
to  disintegration  than  the  others.  Possibly  this  susceptibility  nuiy  have 
been  increased  by  a  somewhat  higher  temi)erature  in  the  intrusive  granite. 

"Of^H.«"  or  Pits  of  Decay. — The  northwestern  jxirtion  of  George  island 
and  the  greater  part  of  the  township  of  Rutherford,  at  the  northwest  ex- 
tremity of  Georgian  bay,  consist  of  red  granite.  Wherever  the  surface 
of  this  rock  has  been  protected  from  glacial  action  it  is  found  to  be  eaten 
into  hollows  in  the  form  of  round  and  sack-like  pits  and  small  caverns. 
The  latter  generally  occur  on  steep  slopes  or  in  per|)endicular  faces  of  the 
rock,  which,  however,  do  not  rise  to  any  great  height  in  this  vicinity. 
The  floors  of  these  caverns  are  usually  flat,  as  they  are  formed  by  the 
lower  sides  of  horizontal  joints,  while  the  roofs  are  arched  like  ovens. 
Whatever  may  have  been  tiie  agency  which  excavated  these  ovens,  it 
always  worked  inward  from  the  granite  face  and  ui)ward  from  the  floor 
formed  by  a  joint,  the  rock  of  the  latter  not  being  afl'ected,  but  remaining 
as  sound  here  as  elsewhere  along  the  joint-plane. 

One  of  these  caverns,  which  occurs  in  the  western  part  of  Killarncy 
village,  opposite  to  George  island  above  mentioned,  and  which  is  shown 
in  figure  1  of  plate  15,  the  rei)roduction  of  a  photograph,  has  almost  the 
form  and  dimensions  of  the  clay  ovens  used  by  the  French  Canadians 
for  baking  bread,  while  other  caverns  in  the  neighborhood  bear  more  or 
less  resemblance  to  this  one;  hence  they  have  received  the  local  name  of 


BULL.  GEOL.  SOC.  AM. 


VOL.  5,  1893,  PL.  15. 


Kli.lllK    1. — "  <.)VKN  "    IN    GkAMTK,    WKST    EnH    Kll.I.ARSEV    VlI.LAHE. 


Kkuhi;  :i.— F.KuiiF.ii  iiuamtk  s-i  ihace  ai'  Kii.lahnkv  Villaue. 


PRE-PALEOZOIC  ROCK   DECAY. 


KVIDENCES    OV   THE    DECAY.  359 

"  ovens,"  whioli  may  also  be  adopted  for  convenience  as  their  peoloj^fic 
desijiniition.  Tlu!  ovon  shown  in  tliis  (i<fure  measures  5  feet  deep,  8  feet 
wide  and  2!  I'ect  high.  Two  men  can  crouch  inside  of  it.  The  door  or 
entrance  i.s  18  inches  high  and  2'\  feet  wide,  which  are  also  about  the 
))rop()rtions  of  the  door  of  a  l)aking  oven  of  the  above  dimensions. 

The  j)its.  which  occur  mostly  upon  the  nearly  horizontal  surface  of  the 
granite,  dilVcr  from  glacial  kettle-holes  in  l)eing  shallower,  seldom  fpiite 
circular  and  in  having  rough  walls.  The  sack-shaped  ovens  are  most  nu- 
merous upon  sloping  surfaces.  In  nearly  every  case  the  fundus  of  these 
hollows  is  pointed  up-hill,  arched  over  by  a  roof  having  a  thin  edge  o 
rather  harder  granite  than  the  general  mass,  and  is  in  the  form  of  a  seg- 
ment of  a  circle.  The  granite  around  these  pits  and  caverns  is  all  bare 
and  exposed  to  the  weather,  but  it  shows  no  decay  or  disintegration 
below  the  iimnediate  surface.  Figure  2  of  plate  lo,  the  reproduction  of 
a  photograph  taken  at  Killarncy  village,  re|)resents  this  condition.  In 
some  places  near  liy  it  is  jiartially  smoothed  and  striated,  as  if  the  glacier 
had  touched  it  very  lightly  and  i)laned  off"  little- spots  here  and  there,  the 
fine  stria;  running  .south  80°  west,  but  at  half  a  mile  to  the  eastward  the 
granite  is  completely  moutonne  and  the  grooves  run  south  40°  west. 

Rocks  ok  tiik  Hukom.w  Belt. 

The  portion  of  lake  Huron  between  the  main  north  shore  and  the 
Manitoulin  chain  of  islands  is  called  the  Xorth  channel.  The  quartzites, 
s(diists,  etcetera,  of  the  great  Huronian  belt,  standing  nearly  on  edge, 
strike  very  regularly  about  east  and  west  for  many  miles  along  the  north 
shore  and  through  numerous  islands  of  this  channel.  A  few  miles  west 
of  La  Cloche  an  intrusive  mass  of  red  granite,  having  a  nearly  circular 
form  and  a  diameter  of  about  four  miles,  interrui»ts  tin;  run  of  the 
(juartzites,  etcetera,  which,  however,  continue  their  regular  east-and-west 
course  on  either  side  of  it.  On  Benjamin  island  the  hills  in  the  central 
part  of  the  granite  intrusion  rise  to  a  height  of  IGO  feet  above  lake  Huron. 
Besting  on  the  southern  Hanks  of  this  island  are  small  areas  of  Black 
river  limestone  near  the  level  of  the  lake,  while  larger  Hat-lying  por- 
tions of  the  same  formation,  constituting  Amedros,  Clapperton  and  Hook 
islands,  ai)proach  the  granite  closely  to  the  east,  south  and  west. 

Ancient  Erosion. 

Typical  Erosion  Sitrface. — Benjamin  island,  which  is  about  two  miles 
long,  consists  of  hummocks  of  granite  of  various  heights  up  to  1(50  feet, 
and  these  present  bluH's  toward  all  points  of  the  compass.     In  many 


'.]()0      K.   liKI.L — l'KI>l'AI,K()Z()IC    DKCAY    OF    CK  YSTA  M,IXK    KOCKS. 

{(hu't.'s  (»n  this  island,  wliuie  the  rock  surface  has  l)een  sheltered  from 
^hicial  action,  wlictlicr  level,  sli>|»in^  or  pi^'pendicular,  it  is  ertxlcd  into 
pits,  hollows,  humniocks  and  knobs  and  has  a  wvy  rou<ih  appearance. 
These  surfaces  hear  a  stron<i  reseinl dance,  on  a  larue  scale,  to  the  pitted 
exterior  of  an  aerolite.  This  is  well  shctwn  in  li<,'ure  1,  a  drawinj^  from  a 
|tliotoij;ra[»h,  which  represents  a  ;_'ranite  surface  on  Henjamin  island. 

The  hollows  sometimes  take  the  form  of  lonji  l»ut  not  deep  caves,  nmler- 
miiiinj^  the  perpendicular  factes  of  steps  in  tins  rock  which  rise  at  inter- 
vals of  ten  to  twei\ty  feet  from  one  iiorizontal  joint  tu  the  next  aliovc 
\t  other  times  tluiy  are  sack-shaped  cavities,  extt^ndinj^  from  a  few  inches 
to  several  feet  into  the  rock.     As  on  (Jeor<ie  islantl.  already  referred  to. 


KKiiuK  \.— Eroded  II  ranite  Surface  near  the  north  End  of  Benjiiiiin  lalami. 


this  form  is  very  common  on  steeply  slopinj?  surfaces,  and  in  these  cases 
the  upper  side  of  each  cavern  is  generally  covered  with  an  arch  wliieh 
thins  away  toward  the  front  (li<?ure  2). 

In  half  a  dozen  cases  ohservcil  on  llenjamin  island,  the  pits  at  various 
heights  from  the  Icjvel  of  the  lake  up  to  KHJ  feet  or  more  were  tilled  ///. 
sitic  with  horizontal  layers  of  the  fossiliferous  Black  river  limestone  like 
that  which  overlies  the  granite  at  lower  levels.  The  limestone  entered 
into  all  the  little  irregularities  of  the  pits  and  adhered  firnd}'  to  their 
walls,  thus  helping  to  retain  its  hold  in  these  cavities  during  the  time 
the  present  surface  has  been  exposed  to  the  weather.  The  little  patches 
constitute  verital)le,  if  minute,  inliers  of  the  Hlaek  river  formation.  The 
limestone  ])rol)al)ly  originally  tilled  all  the  ineiiualities  in  the  granite 


-■*..,■ 


BULL.  GEOL.  SOC.  AM. 


VOL.  5,  1893,  PL.  16. 

1 


KHMltK    1. —  I'n     IN    lillANITK    IIIM'AIMMi    A IIKN  ACKIIl  S    I.HIKSToNK    IN    SIIT. 


V  "J|^^^^^^^r^ 

^^H 

^^'■'^C^.»S 

MP   .  . 

m 

'■^^Ir^:^'^    -W  V 

1 

KllilHK    J.— UaI'    K.\tAVATKl>    AMINO    .loiNTS    IN    liRANITK   TllANSVK.IlSK  T(i    IIIK   ('(llll.SK   ipK   ( il.AII  ATlllN. 


ROCK   DECAY,   DEPOSITION   AND  GLACIATION. 


EROSION. 


stirfac 


861 


n.iKO  an,  ,,,t|„,,.  !!„„,■  ,„.„i,u,l  than  tl,.  s„lToun,ii,«  ,„,s,      Tl 

|.nreiltly  .>!  M)luTctioii„ry  origin.  '"  '"■"  "l'" 

.•n«„n  ab.,v..  .i„«,.ibo<I  toko  pl^.l    '         J l'     ,  "  ''"'  "'"  """'"'" 

.1.. ™..,„ti,„,., ,,oo„,„„ pitte,: , « I ;,"^  „v.'""," """ 7*-»--««- 

■-.»i..i|  ha-i  takon  pla„„  „„  ,,„„,  ^l^MtJ'Z!",'""" 


3()2      U.  BELL— l".{l<:-PALi:0Z01(;   dkcay   ov  ckystallixk  kocks. 


con^jjloniurates.     The  occurrence  of  pure  limestones  in  tlie  i>its  and  ovens 
of  iJenjiunin  island,  in  one  case  in  the  face  of  a  perpendicular  bluff,  as 

well  as  of  the  nearly  horizontal 
beds  of  greater  extent  upon  the 
sound  though  uneven  surface  of 
the  granite,  such  as  might  exist 
at  great  depths  in  the  sea,  but 
not  upon  the  land,  shows  that 

t!;-*UI*J^'''^P^  ^lJ^ ' 'B^l'  Jl-^  '  *''^  ^^^^'^  '^^^  become  thus  eroded 
'm>S^'^*mmJ^^^^'/^i  m'''  :  .1,^1  was  destitute  of  other  cov- 
ering when  the  limestone  began 
to  be  deposited  upon  it.  The 
sea  bottom  then  rose  to  a  more 
moderate  dei)th,  so  that  an 
abundant  fauna  found  a  suita- 
ble hal)itat  and  the  formation 
of  the  limestone  commenced. 
The  area  now  occupied  by  the 
North  channel  of  lake  Huron 
might  at  that  time  have  formed 
a  (juiet  arm  of  the  sea,  with  hills  of  Huronian  rocks  to  the  north,  as  at 
present,  and  similar  hills  to  the  south,  which  have  since  sunk  to  lower 
levels,  but  of  which  traces  remain. 


Fr(iniK  ^.— Low,  circular  liklrie,  four  Feel  in  Diameter, 
im  weathered  Surface  of  Granite. 


I'oNTAcrs  OF  Akchkan  with  Palkozoig  Rocks. 

Along  the  junction  of  the  Arcliean  and  Paleozoic  rocks  occurring  be- 
tween the  foot  of  lake  Ontario  and  tlie  head  o{  Georgian  bay  the  actual 
contact  of  the  Potsdam  sandstone  and  Black  river  limestone  with  the 
Laureniian  gneiss  may  l)e  seen  in  a  great  number  of  places.  The  surface 
of  the  gneiss,  which  can  be  observed  to  pass  under  the  nearly  horizontal 
beds  of  the  newer  rocks,  is  generally  rough  or  angular,  quite  hard  and 
fresh  looking,  as  if  it  had  never  been  exposed  to  weathering  on  land. 
The  points  and  promontories  of  these  flat-lying  strata  which  stretch 
northward  from  the  general  line  of  the  basal  geographic  boundary  of  the 
Sihirian  rocks  in  this  region  lie  on  the  lowest  ground  or  in  the  oro- 
graphic depressions  of  the  southern  margin  of  the  Archean  area,  where 
they  found  shelter  from  glacial  erosion  or  preglacial  decay.  It  is  doubtful 
if  either  these  or  higher  formations  ever  extended  over  a  large  part  of 
the  Archean  area  to  the  northward,  as  is  commonly  supposed,  although 
judging  from  the  vast  amount  of  their  ruins  which  have  been  carried 
si)Uth  they  must  have  been  much  more  extensive  before  the  glacial  epoch 


CONTACTS    OF    ARCHEAN    WITH    PALEOZOIC    ROCKS.  o()o 

than  at  present.  The  middle  Sihirian  inlier  in  the  great  orographic  de- 
pression of  lake  Teniiscaming  on  the  Ottawa,  whicli  will  he  again  referred 
to,  is  {mother* example  of  these  newer  and  undisturbed  strata  oecupying 
ground  much  below  the  general  level  of  the  surrounding  country. 

On  the  north  shore  of  lake  Huron,  between  Killarney  village  and 
Spanish  river,  and  again  on  Grand  Manitoulin  island,  in  the  vicinity  of 
Sheguenda  and  westward  of  that  village,  the  Lower  Silurian  strata  rest 
almost  horizontally  upon  the  flanks  of  hold  l)are  ridges  of  (i[uartzite,  the 
stratification  of  which  stands  nearly  vertically.  The  angh's  of  slope  of 
the  ancient  rock-surfaces  exposed  to  the  weather  along  the  crests  of  these 
ridges  are  continued,  as  far  as  can  be  observed  in  sections,  under  the 
newer  rocks  forming  their  flanks,  so  that  the  former  represent  only  the 
upper  })arts  of  ridges,  once  much  higher,  but  now  ]>artly  buried  under 
the  strata  which  accumulated  around  them  in  Silurian  times.  A  high 
ridge  of  (|uartzite  runs  along  the  north  side  of  Frazer  l)ay.  and  a  similar 
ridge,  but  less  elevated,  forms  the  northwest  side  of  Killarney  bay.  The 
summits  and  sides  of  these  ridges  are,  for  the  most  ])art,  thoroughly 
smoothed  and  striated  by  glaciation,  but  near  their  southern  bases  occa- 
sional spots  are  found  which  have  escaped  the  action  of  tiie  ice  and  wiiich 
show  evidence  of  great  anti(iuity,  the  flinty  rock  being  worn  into  pits 
and  hollows,  but  with  no  sign  of  granular  or  textural  disintegration.  A 
broken  fringe  of  Black  river  limestone  skirts  the  base  of  the  (juartzite 
range  on  the  northwest  side  of  Killarney  bay,  and  the  erosion  of  the 
spots  referred  to  may  be  of  pre-Paleozoic  date,  having  been  preserved  till 
now  by  a  thin  limestone  covering,  or  they  may  rei)resent  portions  of  the 
surface  as  it  existed  immediately  before  the  glacial  epoch  which  have 
escaped  the  smoothing  action  of  the  ice,  hut  this  is  not  so  likely. 

In  the  neighborhood  of  the  quartzite  ridges  only  those  beds  of  the 
newer  rock  which  are  in  contact  with  the  old  formation  contain  angular 
fragments  of  the  rocks  on  which  they  lie.  The  layers  containing  this 
debris  are  usually  of  no  great  thickness  and  the  fragments  themselves 
are  of  small  size;  but  close  to  Sheguenda,  to  the  uortii  and  south  of  the 
village,  are  pretty  thick  strata  composed  of  sharply  angular  pieces  of 
(piartzite  of  all  sizes  packed  closely  and  confusedly  togetlier,  with  only 
enough  calcareous  cement  to  consolidate  them.  Tliis  locality  is  about 
twenty  miles  south  of  the  main  Huronian  area  left  uncovered  by  Silurian 
strata  and  the  water  of  laki;  Huron. 

On  La  Cloche  island  and  elsewhen>  in  the  vicinity  numerous  ridges 
and  domes  of  Huronian  (piartzite  protrude  throu'j;h  the  flat-lying  Silu- 
rian limestones  and  shales,  so  that  the  former  n'scmljle  masses  which 
have  been  forced  up  through  them  from  below,  whereas  they  are  only 
higher  portions  of  the  old  sea  bottom,  around  which  the  horizontal  beds 


o()4      R.  BKLL — rUE-PALE07,0IC    DICrAV    OF   CUYST.VrLIXE    ROCKS. 

of  the  much  newer  rocks  were  dc|)OHite(l.  Tlie  quartzites  appear  to  have 
iindorfronc  no  change  in  texture,  structural  attitucK-  or  even  surface  (!<)n- 
tour  since  a  period  vastly  antedating  Silurian  time.  Such  facts  as  these 
indicate  pretty  clearly  that  the  jdiysical  features  of  the  older  parts  of 
our  continent  had  their  origin  at  a  very  remote  ]teriod. 

RiVKH    AND    LakK   ("haNNRLS    nUK   TO    RoCK    Dkc'AV. 

\  The  writer  has  elsewhere*  shown  that  many  of  the  long,  straight  val- 

leys in  the  Archean  regions  of  Canada,  now  often  occupied  l»y  straight 

I  river  stretches,  by  long,  narrow  lakes,  and  by  inlets  of  the  larger  lakes, 

'  are  due  to  the  decay  and  removal  of  wide  greenstones  dikes  or  of  paral- 

lel dikes,  together  with  the  belts  of  rock  between  them.  Wlien  the 
depressions  along  these  decayed  dikes  are  not  overspread  by  water  they 
form  valleys,  more  or  less  filled  up  with  drift,  so  that  the  greenstone  in  the 
bottom  may  be  only  exceptionally  exposed  to  view.  Copious  si)rings 
fre(][uently  issue  from  the  drift  in  these  valleys. 

The  long,  narrow  and  straight  inlets  of  the  northern  part  of  ( Jeorgian 

;  bay  have  had  their  origin  along  the  courses  of  dikes  of  this  class.     The 

contiimation  of  each  of  these  channels  out  into  the  l)ed  of  the  lake  in 

'  front  of  it  is  distinctly  marked  by  a  straight  line  of  deeper  soundings, 

having  the  same  direction  as  the  fiord  itscilf.  Collins,  Key,  Henvey  and 
Byng  inlets,  each  about  twelve  miles  long,  but  averaging  oid}'  200  or  800 
yards  in  width,  are  good  examples  of  these  fiords.  Among  the  more  con- 
spicuous of  the  long,  narrow  and  nearly  straight  valleys  of  the  Archean 
region  which  have  been  formed  in  the  manner  just  (lescril)ed  may  be 
mentioned  that  of  Onaping  lake,  30  miles  long,  north  of  lake  Huron ; 
Long  lake,  02  miles  long,  north  of  lake  Superior,  and  Sei)iwesk  lake  and 
Nelson  river  below  it,  96  miles  long,  north  of  lake  Winnipeg.  The  green- 
stone of  the  dike  or  dikes  along  the  course  of  these  channels  may  be  seen 
only  on  islets  and  points  or  in  patches  adhering  to  the  country  rock 
on  either  side.     In  the  case  of  fjong  lake  an  immense  greenstone  dike 

,  emerges  from  its  southern  extremity  and  runs  into  the  hills  in  the  same 

j  bearing  as  the  central  line  of  the  lake. 

i  The  course  of  the  Mattagami  river,  the  central  branch  of  the  Moose,  is 

I  guided  in  its  northward  trend  for  a  distance  of  100  miles  from  the  head  of 

lake  Kenogamisse  by  a  number  of  long  dikes  of  greenstone  from  200  to 
1,000  feet  wide,  all  having  nearly  the  same  direction. f  In  a  typical  sec- 
tion of  this  part  of  the  river  we  find  that  the  central  portion  of  the  dike 

i  is  coarsely  crystalline  and  more  deeply  eroded  than  at  the  sides  and 

*  Repoi'tn  Geol.  Survey  Canada,  1870,  p.  ;i31 ;  1875,  p.  315;  1878,  p.  15  CO;  Report  Bureau  of  Mines 
Ontario,  1891,  p.  7(1:  Bull.  Geol.  Soc.  Am.,  1890,  p.  300. 
t  Report  of  R.  Bell :  Geol.  Survey  of  Canada  for  1875,  p.  315. 


KIVKR    AXU    r>AKF    CHANNELS    Dl'K   TO    KOCK    DECAY.  365 

that  it  lias  fjiven  rise  to  tlic  main  channel  of  the  stream.  The  fjnoiss  has 
l)een  altered  and  shattered  for  some  distance  from  the  wallw  of  tlie  dike, 
and  this  has  also  suffered  decay  and  erosion  and  now  forms  a  parallel 
channel  on  either  side  of  the  ceritral  one.  Between  them  the  finer 
f^rained,  hard  and  undecayed  greenstone  constituting  the  outer  portions 
of  the  dike  rises  up  in  the  shape  of  ridges  and  chains  of  Islands,  so  that 
the  river  Hows  as  a  main  central  channel  more  or  less  separated  from 
the  smaller  lateral  ones. 

fjake  Temiscaming,  on  the  Ottawa,  like  the  Montreal  river,  which 
enters  its  southern  extremity,  appears  to  follow  the  course  of  a  great 
decayed  dike  or  set  of  ]»arallel  dikes.  It  lies  in  a  narrow  depression 
which  cuts  across  the  general  strike  of  the  Archean  rocks  of  the  region, 
and  its  surface  is  probably  500  feet  below  the  average  elevation  of  the 
surrounding  country.  Its  width  is  only  from  a  mile  to  two  miles,  and  it 
has  a  length  of  thirty-five  miles,  but  the  channel  is  continued  in  Deep 
river,  the  name  given  to  the  section  of  the  Ottawa  immediately  below"  it. 
Temiscaming  is  an  Ojibwe  word  meaning  "  deep  lake."  and  it  is  well 
named,  for  in  one  part  it  measures,  according  to  Mr  A.  K.  Barlow,  1,800 
feet  in  depth.  The  bottom  is  covered  very  uneijually  with  drift,  which 
has  l)een  pushed  into  it  by  glaciers  at  different  times,  and  the  deepest 
part  of  the  bottom  may  still  be  a  con.siderable  height  above  the  sound 
greenstone  ])elow  this  filling.  If  we  suppose  this  height  to  be  300  feet, 
then  we  have  a  total  of  2,()00  feet  as  representing  the  average  height  of 
the  surrounding  country  al)ove  the  bottom  of  the  excavation.  The  sur- 
face of  the  lake  is  612  feet  above  the  sea,  so  that  the  bottom  of  the  water 
is  about  1,200  feet,  and  that  of  the  whole  rock  excavation  may  be  1,')0() 
feet  or  more  below  this  level.  This  may,  therefore,  be  regarded  as  a  very 
deep  cutting  across  a  country,  the  general  aspect  of  which  is  that  of  a 
mammillated  plateau  with  few  great  inecjualities. 

The  islands  toward  the  north  end  of  the  lake  consist  of  limestone  of 
the  Niagara  formation,  which  also  rises  in  cliffs  at  its  extremity  and 
extends  northward  a  consideral^le  distance  beyond  the  lake  in  the  same 
orogra]ibic  depression,  while  the  Upper  Ottawa  river  falls  over  the  side 
of  this  valley  by  a  rapid  descent  from  the  plateau  to  the  eastward. 

This  valley  therefore  existed  before  the  date  of  the  Niagara  formation, 
an<l  it  is  |)rol)able  that  under  the  limestone  just  mentioned  may  be  found 
older  members  of  the  Silurian  system.  Greenstone  dikes  which  so  fre- 
(piently  cut  the  Archean  rocks  of  northern  ('anada  have  never  been 
found  to  traverse  the  overlying  Silurian,  and  we  are  therefore  warranted 
in  supi)osing  that  the  valleys  which  mark  the  courses  of  the  decayed 
dikes  among  the  former  class  of  rocks  were  mostly  formed  before  the 
deposition  of  the  Paleozoic  strata. 

LI— Bum..'  Ukoi..  Soc.  Am.,  Vol.  fi,  1893. 


.'}(')()     i{.  i{Kr,L — i'kk-pai.kozok;  dwjay  ok  crystallink  kocks, 

AbSKNCK   ok    Vw.KOZniC    DkI'OSITION    and    its   8l(iXIKJCAN(JK. 

The  greater  part  of  the  Archoan  area  referred  to  probably  never  re- 
ceived any  deposit  of  Paleozoic  rocks  upon  it,  so  that  although  nuineroun 
long  and  deep  valleys,  such  as  those  which  have  been  referred  to,  existed 
since  an  earlier  period,  no  evidence  of  such  rocks  ina\'  ever  be  found  in 
the  larger  number  of  them. 

The  depressions  already  mentioned  as  tilled  with  outliers  and  project- 
ing tongues  of  Potsdam  sandstone  and  Black  river  limestone  along  the 
northern  boundary  of  the  Paleozoic  formations  between  Georgian  bay 
and  the  foot  of  lake  Ontario  also  go  to  prove,  as  we  have  seen,  that  the 
surface  of  the  Archean  rocks  had  been  reduced  to  something  like  its 
present  level  and  asjjcct  l^efore  these  beds  were  laid  upon  them. 

EkKKCTS   of   GLACIAL    DkNUDATION. 

In  a  former  i)aper*  the  writer  described  the  effects  of  glacial  denuda- 
tion in  forming  valleys  and  water  channels  along  the  courses  of  ancient 
lines  of  crushing  and  subse(iuent  decay  in  the  crystalline  rocks  north  of 
lake  Huron.  A  similar  effect  has  been  produced  in  this  region,  where 
grou])s  of  ])arallel  joints  run  close  together,  with  a  considerable  breadth 
of  more  solid  rock  on  either  side,  and  where  the  comparatively  thin 
walls  between  them  have  become  softened  by  the  long  continued  pene- 
tration of  surface  water.  It  is  probable  that  the  deep  decay  along  these 
joints  and  lines  of  fracture  took  place  in  pre-Paleozoic  times.  The  dis- 
integrated rock  along  them  was  removed  by  glacial  erosion  with  almost 
equal  facility,  no  matter  what  their  course  may  have  been,  even  where 
the  resulting  channels  are  narrow  and  lie  transversely  to  the  direction  of 
the  excavating  force.  A  good  example  of  this,  on  a  small  scale,  is  shown 
in  figure  2  of  plate  Ifi,  which  is  taken  from  a  i)hotograph  of  a  gap  in 
the  granite  on  George  island,  at  the  northwestern  extremity  of  Georgian 
bay. 

•  »Seo  Report  of  the  Ontario  Bureau  of  Mines,  ISflii. 


I    ^ 


